Select yeast extract

Commercially available solid (powder) reference samples of: cholesterol (Sigma), melanine from Sepia officinalis (Sigma), mannan from Saccharomycs cerevisiae (Sigma), DNA from salmon testes (Sigma), RNA from torula yeast (Sigma), galactoseamine (Merck), N-acetyl galactoseamine (Merck), soy phospholipids (Merck), as well as building blocks of DNA and RNA, i.e., uracil (Merck), thymine (Koch), adenine (CHR), guanine (Sigma), and cytosine (Sigma) were all analyzed at room temperature, without further purification, and after gentle homogenization in a mortar.
Lysogeny Broth (LB) was prepared by adding 10 g/L of Tryptone (Fluka Analytics), 1 g/L of select yeast extract (Sigma life science), 8 g/L of NaCl (≥99.5% purity, Sigma-Aldrich Chemie GmbH), 0.3 g/L of CaCl₂ (97% purity, Fluka Analytics), 1 g/L Dextrose (Biotechnology grade, Amresco) and 2 mg/L Streptomycin (Fluka Chemie GmbH) in ultra-pure water.
The virus dilution buffer (i.e phosphate buffered saline, PBS) was prepared by adding 0.78 g/L NaH₂PO₄ 2H₂O (≥98.0% purity, Sigma-Aldrich Chemie GmbH, Steinheim, Germany) and 0.58 g NaCl (≥99.5% purity, Sigma-Aldrich Chemie GmbH, Steinheim, Germany) in ultra-pure water. The pH was equilibrated to seven using NaOH (≥99% purity, Carl Roth GmbH, Karlsruhe, Germany) and HCl (ACS reagent grade, Sigma-Aldrich, Buchs, Switzerland).

Chitosan—low molecular weight, phosphate-buffered saline tablets, select yeast extract, tryptone, agar, Tween 80, and l-histidine dihydrochloride were purchased from Sigma-Aldrich; acetic acid, sodium chloride p.a., and n-hexane 99% p.a. from Penta Chemicals; sodium tripolyphosphate (TPP) from Acros Organics; ethanol 99.8% for UV/VIS spectroscopy, and glycerol anhydrous g. r. from Lach-Ner; curcumin 99.9% from Chromadex; Brain–Heart-Infusion broth (BHI, Hirn-Herz-Glucose-Bouillon für die Mikrobiologie) from Carl Roth; sunflower lecithin from Fichema s.r.o. Materials for finger replica preparation—FIMO^® soft oven-bake modelling clay and liquid silicon paste with a hardener were purchased from Staedtler.
Antimicrobial foam soap was purchased from Tork. Chlorhexidine digluconate (CHG) 25% w/w aqueous solution was provided by Zentiva, k.s. Two commercially available sanitisers used as a positive control for bacterial testing were purchased in a local store, i.e., ethanol-based gel (72% w/w) from Sanytol and 2% CHG alcoholic solution (IPA 70% v/v) from B. Braun Medical AG.

A colony formation assay was conducted to determine the amount of gut bacteria present in adult Drosophila. Five bacterial culture media were used: brain heart infusion (BHI) broth [18.5 g Bacto BHI (Becton Dickinson 237500), 7.5 g agar and 500 ml distilled water]; lysogeny broth [LB; 10 LB tablets with agar (Lennox, Sigma-Aldrich L7025) and 483 ml distilled water]; de Man, Rogosa and Sharpe (MRS) broth [26 g MRS broth (Oxoid CM0359), 7.5 g agar and 500 ml distilled water]; liver infusion broth [LIB; Difco LIB (Becton Dickinson 226920), 7.5 g agar and 500 ml distilled water]; and mannitol [12.5 g d-Mannitol (Sigma-Aldrich M4125), 1.5 g Bacto Peptone (Beckton Dickinson 211677), 2.5 g select yeast extract (Sigma-Aldrich Y1000), 7.5 g agar and 500 ml distilled water]. The guts of 10 HGD-treated unmated females at 5 days post-eclosion were dissected in 50 mmol l⁻¹ Tris-HCl. The dissected guts were placed in 250 µl of each liquid medium, and the tissues were mashed using a BioMasher (Nippi). The gut sample solutions were diluted 1–1/16. After 5 days of incubation, the number of colonies growing on each plate was counted, and the colony-forming units (CFU) were calculated. The number of replicates used is given in the individual figure legends.